Introduction
Complexometric titrations, also known as complexonometry, are a type of volumetric analysis used to determine the concentration of metal ions in a solution. These titrations are based on the formation of a stable complex between a metal ion (analyte) and a ligand (titrant), commonly ethylenediaminetetraacetic acid (EDTA). Complexometric titrations are widely used in water analysis, metallurgy, and pharmaceutical analysis.
Principle
The principle of complexometric titration is based on the quantitative formation of a metal-ligand complex. The metal ion reacts with a chelating agent to form a 1:1 complex according to the reaction:
- Mⁿ⁺ = metal ion
- EDTA⁴⁻ = tetra-anionic form of EDTA
- The reaction is rapid, stoichiometric, and specific for the metal ion.
The end point is detected using a metal ion indicator, such as Eriochrome Black T, which changes color when all free metal ions have reacted with EDTA.
Types of Complexometric Titrations
- 1. Direct Titration – The metal ion solution is titrated directly with EDTA.
- 2. Back Titration – Excess EDTA is added to the metal solution, and the unreacted EDTA is titrated with a standard solution.
- 3. Replacement Titration – A metal in excess displaces another metal from its complex, which is then titrated.